The present invention relates to a thermal spraying powder containing granulated and sintered particles of an yttrium-aluminum double oxide.
When using a member formed of a material that has low corrosion resistance and oxidation resistance in a corrosive atmosphere or an oxidative atmosphere, a coating formed of a material that has a superior corrosion resistance and oxidation resistance such as an yttrium-aluminum double oxide is generally provided on the surface of the member. For example, Japanese Laid-Open Patent Publication No. 2002-80954 discloses a technique for forming a thermal spray coating of an yttrium-aluminum double oxide on the surface of a base material by plasma spraying granulated and sintered particles of an yttrium-aluminum double oxide.
To suppress corrosion and oxidation of the base material by ambient gas, the thermal spray coating desirably has a high density, or a low porosity. However, if the density is too high, when the thermal spray coating is subjected to a thermal shock, for example, when a heating process with plasma or a heater and subsequent cooling process are repeated, the thermal spray coating is likely to delaminate or detach from the base material. The delamination or detachment of the thermal spray coating occurs often due to the difference between the thermal expansion coefficient of the thermal spray coating and that of the base material made of a material different from the thermal spray coating. Meanwhile, if the density of the thermal spray coating is too low, the base material in the vicinity of the boundary surface between the base material and the thermal spray coating is corroded or oxidized, because the ambient gas reaches the base material through pores in the thermal spray coating. As a result, the thermal spray coating may delaminate or detach from the base material. Furthermore, when a member that has reactivity to the base material (for example, a member made of metal or an alloy) contacts the thermal spray coating, if the density of the thermal spray coating is too low, the member that contacts the thermal spray coating reacts with the base material through pores in the thermal spray coating. As a result, the thermal spray coating may delaminate or detach from the base material.
In this respect, in the technique disclosed in the above publication No. 2002-80954, consideration for the porosity of the thermal spray coating is inadequate. Therefore, it is difficult to obtain a thermal spray coating that is suitable for use where the thermal spray coating is subjected to a thermal shock in a corrosive atmosphere or an oxidative atmosphere and for use where the thermal spray coating is subjected to a thermal shock in a state where the thermal spray coating contacts a member that has reactivity to the base material.